JPH09127333A - Diffraction grating type polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inexpensive diffraction grating type polarizing plate having resistance against dust and to increase the latitude for designing by joining an optical element with an adhesive on the lattice plane of a double refraction diffraction grating. SOLUTION: This diffraction grating type polarizing plate 1 is produced by forming periodical grooves (diffraction grating) 3 on the surface of a crystal substrate 2 having optical anisotropy and joining an optical element 5 with an adhesive to the surface of the substrate 2 where the grooves 3 are formed. As for the crystal substrate 2, for example, a rutile (TiO2 ) having the optical axis in the y-axis direction may be used and grooves 3 are formed along the x-axis. In this case, by selecting the refractive index of the adhesive 4 and depth d of the periodical grooves 3 to satisfy the phase conditions, the light which enters the grating can be divided into two polarized light components perpendicular to each other. Thus, a dielectric material for phase compensation conventionally used is not necessary. Therefore, the diffraction grating type polarizing plate 1 can be produced at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a birefringent polarizing plate that can be used in various optical devices using a semiconductor laser, and more particularly to a diffraction grating type polarizing plate having different diffraction efficiency depending on the polarization direction.

[0002]

2. Description of the Related Art Various conventional diffraction grating type polarizing plates have been proposed. For example, JP-A-63-555
In Japanese Patent Laid-Open No. 01-001, as shown in FIG. 5, a lithium niobate crystal plate 11 having a crystal axis in the x-axis direction has a lattice composed of an ion exchange region and a non-ion exchange region having a cycle in the z-axis direction. What formed 12 is disclosed. Thus, when lithium niobate is subjected to proton ion exchange, the refractive index no with respect to ordinary rays does not change, and the refractive index ne with respect to extraordinary rays rises by about 0.13, and is approximately ne-.
No.

Therefore, the polarization component of the incident light 13 oscillating in the y-axis direction, that is, the ordinary component, has a uniform refractive index in the plane even if the grating 12 is formed by ion exchange, and the optical component is optical. Since there is no effect of the diffraction grating, the 0th-order light 14 is transmitted straight through the crystal plate 11. On the other hand, with respect to the polarized light component vibrating in the z-axis direction of the incident light 13, that is, the extraordinary light component, the refractive index is periodically neg + 0.13 in the proton ion exchange region of the grating 12 and ne in the non-exchange region. Diffracted light 15 and 16
And is emitted from the crystal plate 11.

As described above, by using this polarizing plate, the incident light 13 can be separated into the 0th-order diffracted light and the ± 1st-order diffracted light, and thus the orthogonal polarization component can be separated. Further, since the polarizing plate is formed with the lattice 12 composed of the ion-exchange region and the non-ion-exchange region on the lithium niobate crystal plate 11, it can be made thin and small, and the lithium niobate crystal wafer can be formed. Since it can be produced as a raw material, there is an advantage that it can be mass-produced at low cost by batch processing.

Further, Japanese Patent Laid-Open No. 63-247941 discloses a diffraction grating type polarizing plate as shown in FIG. In this diffraction grating type polarizing plate, a grating groove is formed in an anisotropic plate 17 having a refractive index anisotropy, and in this groove, a refractive index in the direction of the optical axis 18 is ne or a refractive index in the direction orthogonal thereto is ne. No filling material 19 is filled, so that a polarized light component or a parallel component orthogonal to the optical axis 18 is separated as diffracted light. According to this polarizing plate, the grating groove is formed in the anisotropic plate 17,
Since the groove is filled with the filling material 19,
It has the advantage of being compact.

Further, Japanese Patent Laid-Open No. 63-314502 discloses a diffraction grating type polarizing plate as shown in FIGS. 7 and 8. This diffraction grating type polarizing plate is provided in the polarizing plate shown in FIG. 5 in order to cancel the phase change of the ordinary component received by the ion exchange region 23 when transmitting through the grating 22 of the lithium niobate crystal plate 21. In FIG. 7, only the surface of the region other than the ion exchange region 23 is etched to a desired depth, and in FIG. 8, only the surface of the ion exchange region 23 is provided with the dielectric 24 having a desired thickness. . According to such a polarizing plate, it is possible to cancel the phase change of the ordinary light component received in the ion exchange region 23, so that the ordinary light can theoretically be transmitted as 100% as 0th order light.
Therefore, there is an advantage that polarized light can be efficiently separated.

Further, as another conventional diffraction grating type polarizing plate, Japanese Patent Application Laid-Open No. 2-156205 discloses the one as shown in FIGS. 9 and 10. This polarizing plate is formed by periodically arranging grooves 2 on a crystal substrate 25 of lithium niobate.
6 is formed, and the groove 26 is filled with the dielectric 27. According to such a polarizing plate, by changing the depth of the groove 26, it is possible to control the phase difference generated between the ordinary light and the extraordinary light when passing through the convex portion of the groove 26, and the filling amount of the dielectric 27, That is, by changing the thickness, the phase difference between the ordinary light and the extraordinary light generated in the concave and convex portion of the groove 27 can be controlled, so that the degree of freedom can be increased and desired polarization characteristics can be easily obtained.

As still another conventional diffraction type polarizing plate, Japanese Patent Application Laid-Open No. 7-92319 discloses a diffraction grating type polarizing plate as shown in FIGS. FIG.
In the polarizing plate shown in (1), unevenness (grating) is formed on the birefringent substrate 31 by ion etching, and the concave portion is filled with a resin 32 having a refractive index substantially equal to the refractive index of extraordinary light of the birefringent substrate 31. On the grating surface,
Fresnel zone plate 33 formed by molding or the like
Is provided.

According to such a polarizing plate, the resin 3 in which the refractive index of extraordinary light of the birefringent substrate 31 is substantially equal to the concave portion of the etching.
Since 2 is filled, the ordinary light is diffracted to the uneven portion, and the extraordinary light is not diffracted. Therefore, by utilizing this phenomenon, incident light can be polarized and separated into components whose polarization directions are orthogonal to each other. Further, since the Fresnel zone plate 33 is provided on the grating surface, there is an advantage that the lens effect can be obtained.

The polarizing plate shown in FIG. 12 uses lithium niobate (LiNbO ₃ ) as the birefringent substrate 31,
Grating 3 on one surface by proton exchange
4 is formed, a phase compensation film 35 is provided thereon, and a Fresnel zone plate 33 is provided on the grating surface provided with the phase compensation film 35, as in FIG. Even in such a polarizing plate, there is an advantage that the same effect as in FIG. 11 can be obtained.

[0011]

However, FIG.
In the polarizing plates shown in FIGS. 6 and 11, it is impossible to control the phase difference generated between the ion exchange part and the non-exchange part or between the crystal part and the filler part. There is a problem that the degree of freedom is small. On the other hand, the polarizing plates shown in FIGS. 7, 8, 9, 10, and 12 are the positions generated between the ion exchange part and the non-exchange part, or between the crystal part and the filler part. Since the phase difference can be controlled, there is an advantage that the degree of freedom in design is wide, but on the other hand, there is a problem that cost is increased because an etching process and a process for producing a dielectric are added. . In addition, since the diffraction grating surface is exposed in the polarizing plates shown in FIGS. 5 to 10, there is a problem that dust or the like adheres to the grooves having a small pitch forming the diffraction grating to deteriorate the performance.

The present invention has been made in view of the above-mentioned various problems, and an object thereof is to provide a diffraction grating type polarizing plate which is inexpensive, resistant to dust, and has a wide degree of freedom in design. is there.

[0013]

In order to achieve the above object, the diffraction grating type polarizing plate of the first invention is a birefringent device in which grooves are periodically formed on a crystal substrate having optical anisotropy. It is characterized by having a diffraction grating and an optical element bonded to the diffraction grating surface via an adhesive.

Further, the diffraction grating type polarizing plate of the second invention is such that a birefringent diffraction grating in which grooves are periodically formed on a crystal substrate having optical anisotropy and the grooves are filled. It is characterized by having an optical element provided on a diffraction grating surface.

In the first and second aspects of the invention, it is preferable that the birefringent diffraction grating is composed of a birefringent hologram because it can be manufactured easily and at low cost.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. This diffraction grating type polarizing plate 1
Forms a periodic groove (diffraction grating) 3 on the surface of the crystal substrate 2 having optical anisotropy, and joins the optical element 5 with an adhesive 4 on the surface on which the groove 3 is formed. It was done. Here, as the crystal substrate 2, for example, as shown in FIG. 2, rutile (TiO ₂ ) having an optical axis in the y-axis direction is used, and the groove 3 is formed along the x-axis direction.

In the structure shown in FIG. 1, since the crystal substrate 2 has optical anisotropy, ordinary light (polarization component vibrating in the x-axis direction in FIG. 2) and extraordinary light (y in FIG. 2) are used.
The refractive index is different from that of the polarized component that vibrates in the axial direction. Therefore, due to the action of the periodic grooves 3, the diffraction efficiency of the diffracted light generated is different between the ordinary light and the extraordinary light. Here, the cross-sectional shape of the groove 3 is a rectangular wave, and the refractive index of ordinary light is n.
o, the refractive index of extraordinary light is ne, the refractive index of the adhesive 4 is nc,
When the depth of the groove 3 d, and the wavelength lambda, the efficiency E _O 0 of the zero-order light of the ordinary light, ± 1 efficiency E _O 1-order diffracted light of ordinary light, the efficiency of 0-order light of the extraordinary light E _e 0, abnormal Efficiency of ± 1st-order diffracted light E _e
1 is represented by the following formula, where the amount of incident light is 1. In addition, the following calculation formula is "High efficiency of multiple
beam grating "Wai-Hon Lee, Applied Optics Vol.18,
No. 13/1 July 1979 P2153.

[0018]

[Equation 1] E _o 0 = cos ² φ _o (1) E _o 1 = (2 / π) ² sin ² φ _o (2) E _e 0 = cos ² φ _e (3) E _e 1 = (2 / π) ² sin ² φ _e (4) where φ _o = {d (no-nc) / λ} π φ _e = {d (ne-nc) / λ} π

In this embodiment, the incident light 6 is made to act as a polarization beam splitter for separating ordinary light and extraordinary light whose polarization directions are orthogonal to each other. In this case, from the above equation, E _o 0
= 1, E _e 0 = 0, or E _o 1 = 0 and E _e 0 = 1. Therefore, the ordinary light phase term φ _o and the extraordinary light phase term φ
the difference between the _e a _{(φ e -φ o), φ} e -φ o = (l + 1 /
2) π, (where l = 0,1,2,3, ...), and φ _o = mπ / 2, (where m = 0,1,
2, 3, ...) are satisfied.

Here, since l and m can take arbitrary values, many combinations are conceivable. For example, when l = 0 and m = 4, φ _o = 2π, φ _e =
At 5 / 2π, E _o 0 = 1, E _o 1 = 0, E _e 0 = 0, E
_e 1 ≈ 0.41, which makes the incident light 6 the 0th order light 7
And the ± first-order diffracted lights 8a and 8b can be separated into orthogonal polarization components.

In this case, if the crystal substrate 2 is rutile,
The refractive indices no and ne of ordinary light and extraordinary light are wavelength λ = 58.
At 9.3 nm, since no = 2.616 and ne = 2.903, the refractive index nc of the adhesive 4 and the groove depth d are nc.
= 1.468 and d = 1.742λ. As such an adhesive 4, for example, "UV-2100" having a refractive index of 1.477 (trade name; manufactured by Daikin Industries, Ltd.)
Can be used. When m = 5, nc
= 1.755 and d = 1.742λ, so in this case, as the adhesive 4, “BANI-100V” (trade name; manufactured by Maruzen Petroleum Co., Ltd.) is used, and its polyimide and epoxy are mixed. The refractive index may be adjusted to 1.755 by adjusting the ratio.

According to this embodiment, by selecting the refractive index nc of the adhesive 4 and the depth d of the periodic groove 3 so as to satisfy the above-mentioned phase condition, the incident light is made orthogonal to each other.
Since it can be separated into two polarization components, it is not necessary to separately provide a dielectric for phase correction or the like as in the conventional case. Therefore, the diffraction grating type polarizing plate can be made inexpensive. Further, since the optical element 5 is bonded to the diffraction grating surface via the adhesive 4, there is no problem of performance deterioration due to adhesion of dust or the like.

In the second embodiment of the present invention, in the structure shown in FIG. 1, the incident light 6 has an efficiency of 0th-order light of the ordinary light component of 0 and that of the ordinary light and the extraordinary light whose polarization directions are orthogonal to each other. Separation is performed by setting the efficiency of the 0th order light of the component to be 0.8. Therefore, φ _o = (l + 1/2) π, (where l = 0,
1, 2, 3, ...), φ _e −φ _o = (m + 1/2 +
0.148 × p) π, (where m = 0, 1, 2, 3,
.., p = −1, or +1) is satisfied.

Here, since the above l, m and p can take arbitrary values, many combinations are conceivable. For example, if l = 0, m = 0 and p = -1, The refractive index nc of the adhesive 4 and the depth d of the groove 3 are nc = 1.3.
92, d = 1.226λ. An example of such an adhesive 4 is "TFC770" having a refractive index of 1.404.
0 "(trade name; manufactured by Toshiba Silicone Co., Ltd.) can be used.

According to this embodiment, the same effect as that of the first embodiment can be obtained, and since the two orthogonal polarization components have the efficiency of the ± 1st-order diffracted light, the forward path is 0.
The secondary light can also be used in an optical system that uses ± first-order diffracted light in the return path.

FIG. 3 shows a third embodiment of the present invention. In the structure shown in FIG. 1, the diffraction grating type polarizing plate 9 has a refractive index equal to the refractive index nc of the adhesive 4 described above so as to fill the groove portion on the surface of the crystal substrate 2 on which the groove 3 is formed. The optical element 10 included therein is formed by, for example, the 2P method. Therefore, also in this polarizing plate 9, the same effect as that of the above-described embodiment can be obtained.

In the above embodiment, the crystal substrate 2 is used.
The diffraction direction by the periodic grooves 3 formed in the above is the y-axis direction, but this diffraction direction can be any direction. Further, the shape of the groove 3 is not limited to a straight line, and for example, the shape shown in FIG.
As shown in FIG. 5, it is also possible to form a group of curves, which allows the diffracted light to have a lens effect. Furthermore, the crystal substrate 2 in which the groove 3 is formed, that is, the birefringent diffraction grating,
A birefringent hologram can also be used, which makes it possible to obtain a diffraction grating type polarizing plate more inexpensively and easily.

[0028]

As described above, according to the first aspect of the present invention, the optical element is bonded to the grating surface of the birefringent diffraction grating with the adhesive, so that the conventional etching is performed. The diffractive efficiency can be controlled by the refractive index of the adhesive without performing a process or a process of producing a dielectric. Therefore, it is possible to obtain a diffraction grating type polarizing plate that is inexpensive, resistant to dust, and has a wide degree of freedom in design.

Further, according to the second invention, since the optical element is provided on the grating surface of the birefringent diffraction grating so as to fill the groove, the diffraction efficiency is controlled by the refractive index of the optical element. You can Therefore, similarly to the first invention, it is possible to obtain a diffraction grating type polarizing plate which is inexpensive, resistant to dust, and has a wide degree of freedom in design.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a partial detailed view of FIG.

FIG. 3 is a diagram for explaining a third embodiment of the present invention.

FIG. 4 is a diagram for explaining a modified example of the present invention.

FIG. 5 is a diagram showing a configuration of an example of a conventional diffraction grating type polarizing plate.

FIG. 6 is a diagram similarly showing a configuration of another example.

FIG. 7 is a diagram showing a configuration of still another example.

FIG. 8 is a diagram showing a configuration of still another example.

FIG. 9 is a diagram similarly showing the configuration of still another example.

FIG. 10 is a diagram similarly showing the configuration of still another example.

FIG. 11 is a diagram similarly showing a configuration of still another example.

FIG. 12 is a diagram similarly showing the configuration of still another example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diffraction grating type polarizing plate 2 Crystal substrate 3 Groove 4 Adhesive 5 Optical element 6 Incident light 7 0th order light 8a + 1st order diffracted light 8b -1st order diffracted light 9 Diffraction grating type polarizing plate 10 Optical element

Claims (3)

[Claims] 1. A birefringent diffraction grating in which grooves are periodically formed on a crystal substrate having optical anisotropy, and an optical element bonded to the diffraction grating surface with an adhesive. Characteristic diffraction grating type polarizing plate. 2. A birefringent diffraction grating having grooves formed periodically on a crystal substrate having optical anisotropy, and an optical element provided on the diffraction grating surface so as to fill the grooves. A diffraction grating type polarizing plate characterized by. 3. The birefringence diffraction grating is constituted by a birefringence hologram.
The diffraction grating type polarizing plate described.